REFRIGERANT COMPOSITIONS

Abstract: A non-azeotropic refrigerant composition comprising (A) a first component which is a low boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro)fluorocarbons, (hydro)fluorocarbon ethers, hydrocarbons and CO2 and (B) a second component which is a high boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro)fluorocarbons and (hydro)fluorocarbon ethers, the first component (A) and the second component (B) having boiling points which are separated by at least 20 DEG C.

Description: REFRIGERANT COMPOSITIONS The present invention relates generally to non-azeotropic refrigerant compositions and in particular to non-azeotropic refrigerant compositions which are designed to replace chlorodifluoromethane (Refrigerant R-22). Heat transfer devices of the mechanical compression type such as refrigerators, freezers, heat pumps and air conditioning systems are well known. In such devices a refrigerant liquid of a suitable boiling point evaporates at low pressure taking heat from a surrounding zone. The resulting vapour is then compressed and passes to a condenser where it condenses and gives off heat to a second zone. The condensate is then returned through an expansion valve to the evaporator so completing the cycle. The mechanical energy required for compressing the vapour and pumping the liquid may be provided by an electric motor or an internal combustion engine. In addition to having a suitable boiling po ' int and a high latent heat of vaporisation, the properties preferred of a refrigerant include low toxicity, non- flammability , non-corrosivity , high stability and freedom from objectionable odour. Hitherto, heat transfer devices have tended to use fully and partially halogenated chlorofluorocarbon refrigerants such as trichlorofluoromethane (Refrigerant R-ll), dichlorodifluoromethane (Refrigerant R-12), chlorodifluoromethane (Refrigerant R-22), or the azeotropic mixture of chlorodifluoromethane and chloropentafluoroethane (Refrigerant R-115); the azeotrope being Refrigerant R-502. Refrigerant R-22, for example, is widely used in air conditioning systems. However, the fully and partially halogenated chlorofluorocarbons have been implicated in the destruction of the earth's protective ozone layer and as a result the use and production thereof is to be severely limited by international agreement. Whilst heat transfer devices of the type to which the present invention relates are essentially closed systems, loss of refrigerant to the atmosphere can occur due to leakage during operation of the equipment or during maintenance procedures. It is important, therefore, to replace fully and partially halogenated chlprofluorocarbon refrigerants by materials having low or zero ozone depletion potentials. In addition to the possibility of ozone depletion, it has been suggested that significant concentrations of chlorofluorocarbon refrigerants in the atmosphere might contribute to global warming (the so-called greenhouse effect). It is desirable, therefore, to use refrigerants which have relatively short atmospheric lifetimes as a result of their ability to react with other atmospheric constituents such as hydroxyl radicals . Replacements for certain of the chlorofluorocarbon refrigerants presently in use have been developed. These replacement refrigerants tend to comprise selected hydrofluoroalkanes , i.e. compounds which contain only carbon, hydrogen and fluorine atoms in their structure. Thus, refrigerant R-12 is generally being replaced by 1 , 1 , 1 , 2-tetrafluoroethane (HFC-134a). Although replacement refrigerants for R-22 having the required low or zero ozone depletion potential have been proposed, the present inventors realised that in certain heat transfer systems it would be beneficial to replace Refrigerant R-22 with a non-azeotropic refrigerant blend which not only exhibits a low or zero ozone depletion potential but also boils over a reasonably wide temperature range, since in this way the energy efficiency of the system may be improved leading to a reduction in indirect global warming. Non-azeotropic mixtures of this type may, in particular, be usefully employed as the heat transfer fluid in air conditioning units. The present invention provides a non-azeotropic refrigerant composition which is a blend of compounds having low or zero ozone depletion potentials. The refrigerant composition of the invention can exhibit a wide boiling point range and may be used as a replacement for R-22 in air conditioning units. According to the present invention there is provided a non-azeotropic (zeotropic) refrigerant composition comprising: (A) a first component which is a low boiling refrigerant comprising at least one compou ' nd selected from the group consisting of the (hydro ) fluorocarbons , (hydro ) fluorocarbon ethers, hydrocarbons and CO2; and (B) a second component which is a high boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro ) fluorocarbons and (hydro ) fluorocarbon ethers , wherein the low boiling first component and the high boiling second component have boiling points which are separated by at least 20°C. In this specification, a (hydro ) fluorocarbon is a compound selected from the group consisting of the hydrofluorocarbons and the perfluorocarbons and a (hydro ) fluorocarbon ether is a compound selected from the group consisting of the hydrofluorocarbon ethers and the perfluorocarbon ethers. The low boiling first component typically has a boiling point in the range of from -90 to -30°C, preferably in the range of from -70 to -40°C and particularly preferably in the range of from -60 to -45°C. A preferred hydrocarbon for the low boiling first component is propane. The preferred (hydro )fluorocarbons and (hydro ) fluorocarbon ethers for the low boiling first component are selected from the group consisting of trifluoromethane (CHF3), fluoromethane (CH3F), difluoromethane (CH2F2)! pentafluoroethane (CF3CHF2), 1 , 1 , 1-trifluoroethane (CF3CH3), perfluoropropane (CF3CF2CF3), trifluoromethyl difluoromethyl ether (CF3OCF2H) and bis (trifluoromethyl ) ether (CF3OCF3) . The low boiling first component may consist of a single refrigerant compound or it may comprise a mixture of such compounds. Where mixtures of refrigerant compounds are employed for the low boiling first component, they will preferably form an azeotropic or azeotrope-like composition. Preferred azeotropic or azeotrope-like compositions for the low boiling first component include the following: (1) The azeotropic or azeotrope-like composition comprising a mixture, preferably an essentially equimolar mixture, of difluoromethane and pentafluoroethane . (2) The azeotropic or azeotrope-like composition comprising a mixture, preferably an essentially equimolar mixture, of 1 , 1 , 1-trifluoroethane and pentafluoroethane . (3) The azeotropic or azeotrope-like composition comprising a mixture, e.g. an essentially equimolar mixture, of pentafluoroethane and propane . (4) The azeotropic or azeotrope-like composition comprising a mixture, e.g. an essentially equimolar mixture, of trifluoromethyl difluoromethyl ether and propane. (5) The azeotropic or azeotrope-like composition comprising a mixture, e.g. an essentially equimolar mixture, of trifluoromethyl difluoromethyl ether and difluoromethane . (6) The azeotropic or azeotrope-like composition comprising a mixture, e.g. an essentially equimolar mixture, of perfluoropropane and propane . In a preferred embodiment, the low boiling first component comprises at least one refrigerant compound selected from difluoromethane , pentafluoroethane and 1 , 1 , 1-trifluoroethane . Difluoromethane has a boiling point of around -51.7°C, pentafluoroethane has a boiling point of around -48.5°C and 1 , 1 , 1-trifluoroethane has a boiling point of around -47.6°C. In a particularly preferred embodiment, the low boiling first component consists essentially of difluoromethane or an azeotropic or azeotrope-like composition in which difluoromethane is a component. The high boiling second component typically has a boiling point in the range of from -40 to +20°C, preferably in the range of from -30 to +10°C and particularly preferably in the range of from -20 to +10°C. The preferred (hydro )fluorocarbons and (hydro )fluorocarbon ethers for the high boiling second component are selected from the group consisting of 1 , 1-difluoroethane (CHF2CH3) , 1,1,1,2,3,3,3-heptafluoropropane (CF3CHFCF3) , 1,1,1,2,2,3 , 3-heptafluoropropane (CF3CF2CHF2), 1 , 1 , 1 , 2 , 2-pentafluoropropane (CF3CF2CH3) , 1,1,2,2-tetrafluoroethane (CHF2CHF2) , 1,1,1,2,3, 3-hexafluoropropane (CF3CHFCHF2) , 1 , 1 , 1 ,2 ,2, 3-hexafluoropropane (CF3CF2CH2F) , 1,1,1,3,3, 3-hexafluoropropane (CF3CH2CF3) , 1,1,2,2,3, 3-hexafluoropropane (CHF2CF2CHF2 ) , 1 , 1 , 2-trifluoroethane (CHF2CH2F) , 1,1,2,2-tetrafluoropropane (CHF2CF2CH3) , pentafluoroethyl difluoromethyl ether (CF3CF2OCHF2) , 1 , 1 , 1 , 2-tetrafluoroethyl trifluoromethyl ether (CF3CHFOCF3 ) , trifluoromethyl fluoromethyl ether (CF3OCH2F), bis (difluoromethyl) ether (CHF 2 0CHF 2 ), pentafluoroethyl methyl ether (CF3CF2OCH3 ) , 1 , 1 , 2 , 2-tetrafluoroethyl trifluoromethyl ether (CHF2CF2OCF3 ) and perfluorocyclobutane (C F8) . The high boiling second component may consist of a single refrigerant compound or it may comprise a mixture of such compounds, for example an azeotropic or azeotrope-like mixture. In a preferred embodiment, the high boiling second component comprises at least one refrigerant compound selected from pentafluoroethyl difluoromethyl ether, 1 , 1 , 1 , 2-tetrafluoroethyl trifluoromethyl ether, trifluoromethyl fluoromethyl ether, bis (difluoromethyl ) ether, pentafluoroethyl methyl ether, 1 , 1 , 2 , 2-tetrafluoroethyl trifluoromethyl ether, 1,1,1,2,3,3-hexafluoropropane, 1,1, 1,2,2, 3-hexafluoro¬ propane and 1 , 1 , 1 , 3 , 3 , 3-hexafluoropropane . Pentafluoroethyl difluoromethyl ether has a boiling point of around -12°C, 1 , 1 , 1 , 2-tetrafluoroethyl trifluoromethyl ether has a boiling point of around -8°C, trifluoromethyl fluoromethyl ether has a boiling point of around -20°C, bis (difluoromethyl ) ether has a boiling point of around +2°C, pentafluoroethyl methyl ether has a boiling point of around +5°C, 1 , 1 , 2 , 2-tetrafluoroethyl trifluoromethyl ether has a boiling point of around -2°C, 1 , 1 , 1 , 2 , 3 , 3-hexafluoro¬ propane has a boiling point of around +6.6°C, 1 , 1 , 1 , 2 , 2 , 3-hexafluoropropane has a boiling point of around -1.4°C and 1 , 1 , 1 , 3 , 3 , 3-hexafluoropropane has a boiling point of around -1.1°C. In a preferred embodiment, the respective boiling points of the low boiling first component and the high boiling second component are separated by at least 30°C, preferably by at least 40°C. Azeotropic compositions boil at a constant temperature in the evaporator under constant pressure conditions. In contrast, the refrigerant composition of the invention is a non-azeotropic (zeotropic) composition which boils over a temperature range rather than at a constant temperature, and it is this property which tends to reduce the energy required to operate the heat transfer device. The temperature range over which the refrigerant composition of the invention boils is comparatively wide in view of the fairly large difference between the boiling points of the low boiling first component (A) and the high boiling second component (B). Preferably, the refrigerant composition of the invention boils over a temperature range of at least 7°C, more preferably over a temperature range of at least 10°C, and in an especially preferred embodiment the refrigerant composition of the invention will boil over a temperature range of at least 13°C. In a heat transfer device, the refrigerant is used in combination with a lubricant. The lubricant circulates around the device along with the refrigerant and provides for continual lubrication of the compressor. In addition to possessing good lubricity in the presence of the refrigerant, the properties desired of a lubricant include good hydrolytic stability and good thermal stability. Moreover, in order to provide for the return of the lubricant to the compressor, the lubricant should be compatible with the refrigerant, which in practice means that the lubricant and refrigerant should possess a degree of mutual solubility, i.e. the lubricant and the refrigerant should be at least partially soluble in one another. Thus, in accordance with a further aspect of the present invention there is provided a refrigerant/lubricant composition comprising: (1) a non-azeotropic (zeotropic) refrigerant composition comprising: (A) a first component which is a low boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro Jfluorocarbons , (hydro )fluorocarbon ethers, hydrocarbons and CO2; and (B) a second component which is a high boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro ) fluorocarbons and (hydro )fluorocarbon ethers , the low boiling first component and the high boiling second component having boiling points which are separated by at least 20°C; and (2) sufficient to provide lubrication of a lubricant. Suitable lubricants include those comprising a polyoxyalkylene glycol base oil. Suitable polyoxyalkylene glycols include hydroxyl group initiated polyoxyalkylene glycols, e.g. ethylene and/or propylene oxide oligomers /polymers initiated on mono- or polyhydric alcohols such as methanol, butanol, pentaerythritol and glycerol. Such polyoxyalkylene glycols may also be end-capped with suitable terminal groups such as alkyl, e.g. methyl groups. Preferred lubricants are those comprising an ester base oil which comprises at least one neopentyl polyol ester derived from the reaction of at least one neopentyl polyol and at least one aliphatic carboxylic acid or an esterifiable derivative thereof. The preference for these lubricants is due, inter alia, to their generally high level of thermal stability. Suitable neopentyl polyols for the formation of the ester base oil include pentaerythritol , polypentaerythritols such as di- and tripentaerythritol , trimethylol alkanes such as" trimethylol ethane and trimethylol propane, and neopentyl glycol. The esters may be formed with linear and/or branched aliphatic carboxylic acids, such as linear and/or branched alkanoic acids. A minor proportion of an aliphatic polycarboxylic acid, e.g. an aliphatic dicarboxylic acid, may also be used in the synthesis of the ester in order to increase the viscosity thereof. Usually, the amount of the carboxylic acid(s) which is used in the synthesis will be sufficient to esterify all of the hydroxyl groups contained in the polyol, although residual hydroxyl functionality may be acceptable. It will be appreciated that esterifiable derivatives of carboxylic acids may be used in the synthesis if desired. The refrigerant/lubricant compositions of the invention will typically comprise a major amount of the refrigerant and a minor amount of the synthetic lubricant. Preferably, the refrigerant /lubricant compositions of the invention will comprise from 50 to 99 Z by weight, more preferably from 70 to 99 X by weight, of the refrigerant and from 1 to 50 2 by weight, more preferably from 1 to 30 % by weight, of the lubricant based on the total weight thereof.

Claims: C l a ims : 1. A non-azeotropic refrigerant composition comprising : (A) a first component which is a low boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro ) fluorocarbons , (hydro ) fluorocarbon ethers, hydrocarbons and CO2 and (B) a second component which is a high boiling refrigerant comprising at least one compound selected from the group consisting of the (hydro ) fluorocarbons and (hydro ) fluorocarbon ethers , wherein the low boiling first component and the high boiling second component have boiling points which are separated by at least 20°C. 2. A refrigerant composition as claimed in claim 1 wherein the low boiling first component (A) has a boiling point in the range of from -90 to -30°C. 3. A refrigerant composition as claimed in claim 1 or claim 2 wherein the low boiling first component (A) comprises propane. 4. A refrigerant composition as claimed in any one of claims 1 to 3 wherein the low boiling first component (A) comprises at least one compound selected from the group consisting of trifluoromethane , fluoromethane , difluoromethane , pentafluoroethane, 1,1,1-trifluoroethane, perfluoropropane, trifluoromethyl difluoromethyl ether and bis ( trifluoromethyl ) ether. 5. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) comprises at least one refrigerant compound selected from difluoromethane , pentafluoroethane and 1,1, 1-trifluoroethane . 6. A refrigerant composition as claimed in claim 4 or claim 5 wherein the low boiling first component (A) consists essentially of difluoromethane or an azeotropic or azeotrope-like composition in which difluoromethane is a component. 7. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of difluoromethane and pentafluoroethane. 8. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of 1 , 1 , 1-trifluoroethane and pentafluoroethane. 9. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of pentafluoroethane and propane. ιo. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of trifluoromethyl difluoromethyl ether and propane . 11. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of trifluoromethyl difluoromethyl ether and difluoromethane. 12. A refrigerant composition as claimed in claim 4 wherein the low boiling first component (A) is an azeotropic or azeotrope-like composition comprising a mixture of perfluoropropane and propane. • 13. A refrigerant composition as claimed in any one of claims 1 to 12 wherein the high boiling second component (B) has a boiling point in the range of from -40 to +20°C. -* 14. A refrigerant composition as claimed in any one of claims 1 to 13 wherein the high boiling second component (B) comprises at least one compound selected from the group consisting of 1 , 1-difluoroethane (CHF2CH3) , 1,1,1,2,3,3,3-heptafluoropropane (CF3CHFCF3), 1, 1 ,1,2,2, 3 , 3-heptafluoropropane (CF3CF2CHF2) , 1 , 1 ,1 , 2 , 2-pentafluoropropane (CF3CF2CH3), 1,1,2, 2-tetrafluoroethane (CHF2CHF2) , 1,1,1,2,3, 3-hexafluoropropane (CF3CHFCHF2) , 1 ,1 , 1 , 2 , 2 , 3-hexafluoropropane (CF3CF2CH2F) , 1 , 1 , 1, 3 , 3 , 3-hexafluoropropane (CF3CH2CF3), 1,1,2,2,3,3-hexafluoropropane (CHF2CF2CHF2) , 1 , 1,2-trifluoroethane (CHF 2 CH 2 F) , 1 , 1 , 2 , 2-tetrafluoropropane (CHF2CF2CH3) , pentafluoroethyl difluoromethyl ether (CF3CF2OCHF2 ) , 1 , 1 , 1 , 2-tetrafluoroethyl trifluoromethyl ether ( CF3CHFOCF3 ) , trifluoromethyl fluoromethyl ether (CF3OCH2F), bis (difluoromethyl ) ether (CHF2OCHF2), pentafluoroethyl methyl ether (CF3CF2OCH3 ) , 1 , 1 , 2 , 2-tetrafluoroethyl trifluoromethyl ether (CHF2CF2OCF3 ) and perfluorocyclobutane (C4F8). 15. A refrigerant composition as claimed in claim 14 wherein the high boiling second component (B) comprises at least one compound selected from the group consisting of pentafluoroethyl difluoromethyl ether, 1 , 1 , 1 , 2-tetrafluoroethyl trifluoromethyl ether, trifluoromethyl fluoromethyl ether, bis ( difluoromethyl ) ether, pentafluoroethyl methyl ether, 1 , 1 , 2 , 2-tetrafluoroethyl trifluoromethyl ether, 1,1,1,2,3,3-hexafluoropropane, 1,1,1,2,2, 3-hex fluoro- propane and 1 , 1 , 1 , 3 , 3 , 3-hexafluoropropane . 16. A refrigerant composition as claimed in any one of claims 1 to 15 wherein the respective boiling points of the low boiling first component (A) and the high boiling second component (B) are separated by at least 30°C. 17. A refrigerant composition as claimed in claim 16 wherein the respective boiling points of the low boiling first component (A) and the high boiling second component (B) are separated by at least 40°C.

Inventors: CORR STUART, MURPHY FREDERICK THOMAS, POWELL RICHARD LLEWELLYN, CORR, STUART, MURPHY, FREDERICK, THOMAS, POWELL, RICHARD, LLEWELLYN
Applicants: CORR STUART, ICI PLC, MURPHY FREDERICK THOMAS, POWELL RICHARD LLEWELLYN, CORR, STUART, IMPERIAL CHEMICAL INDUSTRIES PLC, MURPHY, FREDERICK, THOMAS, POWELL, RICHARD, LLEWELLYN
Application year: 1994
Main classification: C09K5
IPC codes: C09K5